AST101-2nd.docx

September 15 , 2011
AST101
- all assignments due Tuesday at 11:59 pm
 The solar system is HUGE and the vast majority of it is empty (tiny quantities
of gas and dust fill the space)
 1 AU (distance between sun and earth) = 1 Astronomical Unit
 (Mercury is 0.4 AU, Venus is 0.7 AU, Mars is 1.5 AU)
1 AU
= 1 Astronomical Unit = 1.5 x 1011m
= average distance between Earth and the Sun
 light year is measure of distance (distance light travels in a year)
 sun and nearest start – 4.4 light years
 1 ly= 1 light year
= 9.46 x 10^12 km
= distance light travels in one year
 1 AU = 8 light minutes (for light to get from earth to sun)
 light travels at a finite speed
 so, no matter where you look, you are looking back in time
 The Andromeda Galaxy is 2.5 million ly away.
o It’s the nearest large galaxy to the Milky Way
 The galaxy NGC 4696 is about 150 million light years away
 Stars are balls of plasmawhich produce energy by nuclear fusion.
 Planets are rocky, icy, or gassy, and they don’t prod